1. Field of the Invention
The present invention relates to a thin ceramic green sheet and to a method for producing the same and, more particular, to a ceramic green sheet containing a urethane resin (polyurethane) and a method for producing the same.
2. Background Art
Hitherto, there have widely been known methods in which a plurality of ceramic green sheets each containing a ceramic powder and an organic binder are formed and subjected to processes such as mechanical working, printing, stacking, and firing, to thereby produce a variety of finished products. Japanese Patent Application Laid-Open (kokai) No. 2006-121012 discloses such a method.
Conventionally, ceramic green sheets are generally produced by the following technique. First, a ceramic powder is mixed with a solvent, a dispersion medium, and an organic binder, thereby preparing a ceramic slurry, and the ceramic slurry is molded into a thin sheet through, for example, the doctor blade method. The thin molded product is dried to evaporate the solvent, thereby producing a thin ceramic green sheet. The produced green sheet has a residual solvent content of less than 1%.
As shown in FIG. 3, in the thus-produced ceramic green sheet, the intermolecular distances between organic binder molecules tend to decrease with the progress of evaporation of the remaining solvent during a process which involves heating. Thus, the ceramic green sheet has a problem of tendency to easily (heat)-shrink; i.e., exhibits a large percent (heat) shrinkage.
With ceramic green sheets exhibiting a large percent (heat) shrinkage, high positioning accuracy is difficult to obtain, in the cases of, for example, printing or drying of ceramic green sheets and stacking of a plurality of ceramic green sheets. Thus, there is demand for reduction of heat-induced percent shrinkage of ceramic green sheets.
Furthermore, in order to facilitate subsequent processes such as mechanical working and firing, ceramic green sheets are required to satisfy plasticity (i.e., cracking resistance to bending), punching property (i.e., resistance to cracking in a section formed by punching), and sinterability (ease of dense sintering). Therefore, provision of a ceramic green sheet having plasticity, punching property, and sinterability of satisfactory levels as well as a low percent (heat) shrinkage is desired.